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A Spanish-Italian research team has investigated different configurations of bifacial agrivoltaic solar systems deployed in olive groves and has discovered that the inclination angle of the solar modules has a significant impact on energy performance, while their height plays a crucial role in the increased agricultural yield.
A group of scientists from the University of Jaén (Spain) and the Sapienza University of Rome (Italy) has investigated how to combine bifacial agrovoltaic systems with olive cultivation to improve both energy and agricultural production. “Considering three different varieties of olive trees (Picual, Manzanilla and Chemlali) and exploring various configurations of bifacial photovoltaic systems, the research aims to optimize the overall yields of energy generation and olive production,” the researchers explain.
“Contrary to conventional expectations, the vertical inclination of the photovoltaic modules is optimal for maximizing the yield of olive trees,” corresponding author Elmehdi Mouhib told pv magazine . “This unexpected finding highlights the nuanced interaction between the orientation of photovoltaic modules and the agricultural productivity of olive trees within agrivoltaic systems.”
The research group tested different configurations of the system depending on the angle of inclination and height of the solar modules. The scenarios were analyzed in a simulation computer program and modeled using the ray tracing method, which takes into account how light interacts with objects.
For the simulations, the academics assumed a bifacial agrovoltaic system operating in the southern Spanish city of Jaén, with the irradiance and temperature values ??of a typical meteorological year. The simulated farm had an area of ??860 m2, corresponding to a rectangular shape with a length of 41.42 m and a width of 20.76 m. It housed eight rows of olive trees and seven photovoltaic rows in a super-intensive farming approach.
“In this type of olive cultivation, the trees are usually arranged in a rectangular shape with a planting pattern of 4-5 m × 2-3 m, which leaves enough space between rows to house photovoltaic modules,” they explain. “Super-intensive plantations require moderately sloping soils, which facilitate the installation of photovoltaic structures.”
In their simulation, the tree trunks have a radius of 0.25 m and a height of 1 m, while the crown has a radius of 1 m and a height of 1.5 m. The total height is considered to be 2.5 m, which represents the average height of the olive trees in this cultivation approach. The bifacial models were assumed to have a size of 1.755 m x 1.038 m and were placed in cubes with a minimum height of 3 m to ensure the movement of the collection machines.
“The amount of solar radiation that reaches the rear face of the bifacial photovoltaic module is directly related to the albedo coefficients of both the trees and the soil,” the scientists add. “In this study, the broadband albedo used for trees is 0.309. Additionally, light soil was used as the soil albedo with a broadband albedo of 0.25”.
The temperature was set at 21ºC and the humidity at 40%, and the simulation assumed 16 hours of light per day. To calculate the yield of olive trees, the response of gross carbon assimilation to absorbed light was evaluated. That indicates the quantum efficiency of photosynthesis in olive trees, showing how well they convert light energy into chemical energy.
Each configuration was measured with tilt angles of 0, 20, 40, 60, 80 and 90 degrees, and hub heights of 3 m, 3.5 m, 4 m and 4.5 m. The three olive tree varieties were chosen due to their different responses to light, as they are prevalent in various geographical areas. Picual olives are predominantly found in Jaén, Manzanilla olives are endemic to Seville and Chemlali olives can be found in several Mediterranean countries, particularly Tunisia.
“Overall, the results indicate that the variation in the tilt angle has a greater impact on the photovoltaic performance, while the variation in the height of the photovoltaic module mainly affects the performance of the olive trees,” the researchers stated. “The findings indicate that PV modules tilted near the latitude of the site achieve the highest energy yield, while modules oriented vertically lead to the highest olive yield.”
The maximum land equivalence ratio (LER), which quantifies the land productivity of combined energy and crop production, was 171% of what each system would produce if implemented separately in the same area. It was achieved with an inclination angle of 20 degrees and 3 m. The lowest LER was reached at 90 degrees, at a height of 4 m.
“The evaluation of olive varieties reveals a moderate dependence on shading, making all varieties suitable candidates for agrivoltaic applications,” the researchers conclude.
The results were presented in the article “ Enhancing land use: Integrating bifacial PV and olive trees in agrivoltaic systems,” published in Applied Energy . |
